Quenching process



United States Patent 3,498,850 QUENCHING PROCESS Ronald W. Morton,Didcot, Berkshire, England, assignor to Esso Research and EngineeringCompany, a corporation of Delaware No Drawing. Filed Feb. 6, 1967, Ser.No. 614,035

Int. Cl. C21d ]/58 US. Cl. 148-18 9 Claims ABSTRACT OF THE DISCLOSURE,to which has been added from about 2 to about 15 weight percent, on atotal composition basis, of a sulfur-containing derivative of an alkalimetal salt or alkaline earth metal salt of an alkyl phenol, an alkylthiophenol, or an alkyl phenol thioether, wherein the alkyl groups havefrom 5 to 30 carbon atoms. The sulfur-containing derivative can beobtained by reacting the metal salt with elemental sulfur or by reactingthe metal salt with a phosphosulfurized hydrocarbon such asphosphosulfurized polyisobutylene. Additional metal over and above thataccounted for by the said metal salt may be present, e.g. in the form ofdispersed metal carbonate. The quench oil can also contain from 2 to 15weight percent of metal organic sulfonate.

This invention relates to a process for quenching metals, especially themar-quenching of low alloy steel through hardening; and low alloy casehardening steel.

With ever-increasing competition many industries, especially the motorcar industry, have been seeking ways to cheapen their process .ofproducing high quality hardened components such as gears, or pinions. Inparticular attention has been directed towards the production of highquality products from the cheaper and more readily available low alloysteels, such as B.S. En 31, 32, 35, 42, 44, 351, 352, 353, 363 and SAE1019, 4620, 8615, 8617, 52100 and 8620 steels. These products are nearlyalways produced by forming accurately, then hardening by heating themetal, e.g. steel, to high temperature and then plunging the metalrapidly into a bath of a liquid maintained at a certain temperature orwithin a certain temperature range. In order to reach the requireddegree of hardness without distortion, cracking or wide variations inhardness from batch to bath, and to obtain a hardened metal ofconsistent and satisfactory core hardness, and to obtain satisfactoryoil life, it is necessary that the process be carefully controlled andthat the quenching liquid should meet fairly stringent requirements. Theliquid should have a high flash point, good thermal stability, longlife, very high cooling rate over the critical tempera- -ture range downto about 500 C., good metal hardening characteristics and should notcause thick deposits to be left on the metal after removal from thequenching bath. The liquid should also be capable of rapidly absorbingheat from the hot metal so that the quenching time is reduced. Hitherto,the quenching of metals using the quenching oils on the market has notmet all these stringent requirements. However, a process has now beendiscovered whereby many if not all the previous difliculties have beenovercome.

According to the process of the invention a metal is quenched or pressquenched by heating the metal to an elevated temperature, and thereaftertransferring the 3,498,850 Patented Mar. 3, 1970 metal into a bath ormould containing a liquid maintained at a temperature lower than theelevated temperature, wherein the liquid comprises a major proportion byweight of an oil, e.g. a hydrocarbon oil, and a minor proportion byweight of a phenol-based detergent additive (as hereinafter defined).

The process of the invention can be applied to the quenching of anymetal or metal alloy, but is especially suitable for quenching throughor case hardened steels, e.g. a steel having a carbon content, at leastat the surface, of about 0.9% by weight. Other suitable metals includealuminum alloys.

The elevated temperatures to which the metal is first heated and soakedwill depend on the nature of the metal, but generally this temperaturewill be at or above the temperature where the impurities or alloyingelements are in solid solution. Thus, in the case of carbon steel thiselevated temperature will be above 800 C. and often about 900 C.,whereas with aluminum alloys, e.g. duraluminium, this elevatedtemperature will be of the order of about 500 C.

The temperature of the liquid in the bath into which the metal isplunged will vary according to the treatment it is desired to give tothe metal. Thus, in the case of carbon steel (e.g. 0.9 to 1.2% by weightcarbon) if it is desired to marquench the steel, the temperature .of theliquid in the bath will be maintained at about 150 C. to 250 C., e.g.about 200 C. depending upon the Ms point of the particular steel. Ifhowever, it is desired to cold quench the steel the temperature of theliquid will be from ambient to about 60 C. Cold quenching of steel willnormally result in a more rapid quench than marquenching, but there willbe more difference in mechanical properties between the core and case ofthe metal. For warm quenching of steels the temperature of the liquidwill usually be from 60 C. to 250 C. When quenching aluminium alloys,the temperature of the liquid in the bath will often be about ambient.

The metal should be transferred or plunged into the bath as quickly aspossible. The bath may be a tank or any receptacle suitable forcontaining the liquid and also large enough to accommodate the metalwhich is being quenched. Generally the metal will completely immersed inthe liquid whilst it is being quenched until the case/core temperaturedifferential is small enough to prevent internal stresses being set upduring subsequent conversion to martensite (in the case of steel) ormixed structures on cooling in air or by water spray to ambienttemperature. The quench bath may be covered or uncovered, and may bemaintained under an inert atmosphere preferably an endothermic gas.

The oil may be a synthetic oil, e.g. a polyglycol ether or ester, but isgenerally a hydrocarbon oil. The hydrocarbon oil is preferably adistillate mineral oil of medium viscosity. For cold quenching,naphthenic or mixed base distillates of medium to low viscosity aresuitable. For marquenching especially suitable mineral oils areparaffinic distillates having a KV at 210 F. of between 9.0

and 14.0, e.g. about 12.5, a viscosity index of between and 105, e.g.about 100, and a flash point of at least 250 C., e.g. about 280 C.

In general it has been found that close out high flash point (e.g. above250 C., and preferably above 270 C.) middle distillates are the mostsuitable hydrocarbon oils.

The phenol-based detergent additive contained in a minor proportion inthe hydrocarbon oil is defined as the reaction product of sulphur or asulphur-containing compound with either (1) an alkyl phenol or alkylphenol sulphide and an alkali metal or alkaline earth metal base, or (2)an alkali metal or alkaline earth metal alkyl phenate or alkylthiophenate.

Thus, the detergent additive may be alkaline earth meta1 (e.g. barium)sulphurised phenate or an overbased alkaline earth metal (i.e. barium)sulphurised phenate. Such phenates are prepared by reacting an alkalineearth metal alkyl phenate with elemental sulphur to give a complexreaction product, free alkyl phenol or volatile material in the reactionproduct preferably being removed by steam distillation. The alkylphenate can be prepared by reacting the corresponding alkyl phenol, e.g.octyl or di-octyl phenol, with an alkali metal base or preferably analkaline earth metal base, e.g. barium octahydrate. The reaction betweenthe phenate and sulphur is conducted at elevated temperature, andpreferably in the presence of an inert gas,

e.g. nitrogen. A preferred method of making this type of phenol-baseddetergent additive is described in British patent specifications 697,461and 720,372.

The more preferred types of phenol-based detergent additives are thoseprepared by reacting either (1) an alkali metal or alkaline earth metalbase with an alkyl phenol or alkyl phenol sulphide and aphosphosulphurised hydrocarbon in the presence of a diluent oil, or (2)an alkali metal or alkaline earth metal alkyl phenate or alkylthiophenate with a phosphosulphurised hydrocarbon in the presence of adiluent oil. In both cases (1) and (2) it is preferable if carbondioxide is blown into the reaction mixture whilst the reaction takesplace.

Suitable alkyl phenols or alkyl phenol sulphides include mono orpolyalkyl compounds in which each of the alkyl groups contains between 5and 30, e.g. 8 to 26 carbon atoms. Particularly suitablephosphosulphurised hydrocarbons are phosphosulphurised polyolefins, e.g.polybutene, having a molecular weight of from 100 to 50,000 e.g. about900. Methods of preparing these phenol-based detergent additives aredescribed in British Patent specifications 921,124; 940,175; 958,520;970,786; 867,800 and 887,334. This type of phenol-based detergentadditive, i.e. prepared by a reaction involving a phosphosulphurisedhydrocarbon, is preferably highly basic, e.g. having an alkalinity indexgreater than 50. This of course may be achieved by ensuring that thereis excess base in the reaction mixture. Generally, it is preferable ifthese additives are derived from alkaline earth metal base, especiallyfrom barium pentahydrate or barium octahydrate.

The quantity of phenol-based detergent additive incorporated in thequenching liquid is preferably less than 20% by weight, and a suitableamount has been found to be about by weight, based on the combinedweight of hydrocarbon oil and phenol-based detergent additive.

It is also been found that very often the thermal stability andquenching speed of the quenching oil may be improved if in addition tothe phenol-based detergent ad ditive, a minor proportion by weight of analkali metal or alkaline earth metal sulphonate is present. Thissulphonate is preferably highly basic, and alkaline earth metal, (e.g.calcium) sulphonatesof high basicity, e.g. having an alkalinity index ofabout 300 have been found to be particularly suitable.

The amount of sulphonate incorporated in the quenching liquid ispreferably less than by weight based on the total weight of quenchingliquid and may be the same as that of the phenol-based detergent.

A minor proportion by weight based on the total weight of quenchingliquid e.g. 0.005% by weight, of an antifoaming agent, for example asilicone, may be used.

Particularly suitable quenching oils have been found to be:

Composition, wt./wt. percent Phenol-based detergent sulphonateHydrocarbon oil additive additive The invention is now described withreference to the following examples, in which the base hydrocarbon oilused was paraflinic distillate of medium viscosity having the followingproperties:

KV 210 F 12.7 V.I. 100 Flash point C. 277

The phenol based detergent additive which was used .in the examples wasthe reaction product obtained as follows; 14.5 wt. percent of aphosphosulphurised polybutene of molecular weight 750 to 900 having asulphur content of 6.1 to 6.5 wt. percent and a phosphorus content of3.2 to 3.7 wt. percent was mixed with 7.4 wt. percent of a mixtitre of Cto C alkyl phenols in 46.7 wt. percent of a mineral hydrocarbon diluentoil. This mixture was purged with nitrogen from to 133 C. and continuedat a temperature of 127 to 135 C. 26.9 wt. percent of bariumpentahydrate was added over 3 to 6 hours. Half an hour after the startof the barium pentahydrate addition carbon dioxide was blown in. Theblowing in of CO was continued for about half an hour after the last ofthe barium pentahydrate had been added and in all 4.5 wt. percent of COwas added. Finally the reaction product was obtained by filtering.

The alkaline earth metal sulphonate detergent additive used in theexamples was an overbased calcium sulphonate prepared as follows:Calcium carbide was added to methanol and carbon dioxide bubbledthrough. The reaction mixture thus obtained was added to the calciumsalt of a polyalkylated benzene sulphonic acid, the calcium salt havingMW of about 800, and the alkyl group being C A complex was formed andthis was treated with steam whereby the complex decomposed. The requiredoverbased calcium sulphonate was obtained by filtering.

EXAMPLE I steel after quenching were as follows:

Surface hardness VPN 840 Core hardness VPN 750 EXAMPLE -II The procedureof Example I was repeated except that the quenching liquid consisted of90% by Weight of base hydrocarbon oil, 5% by weight of the phenol-baseddetergent additive and 5% by weight of the overbased calcium sulphonate.

The mechanical properties of the steel after quenching were as follows:

Surface hardness VPN 800 Core hardness VPN 720 EXAMPLE III The procedureof Example I was repeated except that the quenching liquid consisted of96% by weight of base hydrocarbon oil, 2% by weight of the phenol-baseddetergent additive and 2% by weight of the overbased calcium sulphonate.

The mechanical properties of the steel after quenching were as follows:

Surface hardness VPN 840 Core hardness VPN 750 EXAMPLE IV The procedureof Example I was repeated with a very crltical 1% diameter SAE 8620 casehardened steel using the same quenching liquid as in Example II. Thecore hardness was 300-390 VPN. The specification requirement (240-320VPN) could not be achieved with other oils containing prior art quenchspeed improver, so that the quench oils of this invention showed greatimprovement.

EXAMPLE V The process of Example I was repeated with a casecarburised 1/2" diameter CM 60 bar using the same quenching liquid as in Example 11.The core hardness was found to be 330 VPN.

EXAMPLE VI The process of Example V was repeated using a casecarburised1 /8 diameter SAE 8615 bar. The core hardness was found to be 281 VPN.

What is claimed is:

1. In a process for the quenching of a metal wherein said metal is firstheated and its temperature is then lowered rapidly by immersion in aliquid quenching bath, whereby desired metallurgical changes areefiected in said metal, the improvement which includes using as thequenching bath a liquid composition comprised of a major proportion ofan oil having a flash point of at least 250 C., to which has been addedfrom about 2 to about 15 weight percent, based on said composition, of asulfur-containing derivative of an alkali metal salt or alkaline earthmetal salt of an alkyl phenol compound having alkyl groups of from about5 to 30 carbon atoms, said alkyl phenol compound being an alkylatedphenol, an alkylated phenol thioether, or an alkylated thiophenol, saidsulfur-containing derivative being fur ther characterized in that it isthe product of reaction of said alkali metal salt or alkaline earthmetal salt with elemental sulfur or with a phosphosulfurized hydrocarbonof from 100 to 50,000 molecular weight.

2. Improvement as defined by claim 1 wherein said oil is a hydrocarbonoil.

3. Improvement as defined by claim 1 wherein said oil is a parafiinicdistillate having a kinematic viscosity of 6 from 9 to 14 at 210 F. anda viscosity index of from to 105.

4. Improvement as defined by claim 1 wherein said phosphosulfurizedhydrocarbon is phosphosulfurized polybutene.

5. Improvement as defined by claim 1 wherein said sulfur-containingderivative has associated therewith an alkali metal or alkaline earthmetal carbonate.

6. Improvement as defined by claim 1 wherein said liquid compositionalso contains from about 2 to about 15 weight percent based on saidcomposition, of an alkali metal or alkaline earth metal organicsulfonate.

7. Improvement as defined by claim 1 wherein said sulfur-containingderivative is the product of reacting phosphosulfurized polybutene withthe barium salts of C to C alkyl phenols, said derivative includingdispersed barium carbonate.

8. Improvement as defined by claim 1 wherein said liquid compositioncontains from about 2 to about 5 weight percent of an overbased alkalineearth metal salt of a polyalkylated benzene sulfonic acid.

9. Improvement as defined by claim 1 wherein said metal is carbon steel.

References Cited UNITED STATES PATENTS 1,310,020 7/1919 Huestis 252732,536,403 1/1951 Wallace et al. 148-29 2,848,362 8/1958 Flemment et al.14829 2,866,729 12/1958 Zimpel 252-73 3,159,510 12/1964 Rozalsky 14828 rHYLAND BIZOT, Primary Examiner 0 T. R. FRYE, Assistant Examiner s. (:1.X.R.

